An apparatus such as a film forming apparatus and a sputtering apparatus, using plasma generated in a chamber, incorporates two electrodes (targets), and this kind of apparatus applies voltage in a manner referred to as a “dual cathodes system” that applies cathode-voltage and anode-voltage to the electrodes (targets), switched alternately, thereby generating plasma (see the patent document 1).
FIG. 9A illustrates schematically voltage application according to the dual cathodes system. The configuration shown in FIG. 9A is provided with two electrodes (targets) 101 and 102 disposed in a chamber, a radio frequency power source 103 configured to apply radio frequency voltage to the electrode (target) 101, a radio frequency power source 104 configured to apply radio frequency voltage to the electrode (target) 102, and a switching unit 105.
The switching unit 105 performs switching between the radio frequency power source 103 and the radio frequency power source 104, so as to feed alternately radio frequency voltage outputs with different polarities, to the electrode 101 and the electrode 102, respectively. The radio frequency voltage outputs in antiphase with each other are applied, respectively to a pair of electrodes, that is, while applying cathode voltage to one electrode, anode voltage is applied to the other electrode. Similarly, while applying anode voltage to one electrode, cathode voltage is applied to the other electrode.
By applying the radio frequency voltages in antiphase with each other, electric charges accumulated in the electrode 101 and the electrode 102 are canceled, thereby maintaining stable plasma (see Patent Document 1).
FIG. 9B illustrates a configuration including one radio frequency power source for applying voltage in a dual cathodes system. The configuration as shown in FIG. 9B is provided with two electrodes (targets) 111 and 112 disposed in a chamber, one radio frequency power source 113 for applying radio frequency voltage to the electrodes (targets) 111 and 112, a switching circuit 115 for applying radio frequency voltage to each of a pair of the electrodes 111 and 112, alternately by switching, and an AC power source 116 for applying AC voltage to each of the electrodes in such a manner that cathode and anode are replaced by each other between the pair of the electrodes (targets).
In this configuration, the radio frequency power source 113 is commonly used for the pair of the electrodes (targets), and the radio frequency voltage outputs generated by the radio frequency power source 113 are applied, being superimposed on AC voltage generated by the AC power source 116, in such a manner as alternately switched between the electrodes (targets) (see Patent Document 2).